A column of air, contained within a tube, can be vibrated to produce a sound, by properly directing an air stream cross-wise over an open end of the tube. Where the tube is continuous, without any side openings and with the opposite end closed, the basic inside tube length and diameter determine the primary and secondary resonant vibrations, or tones, generated in the tube. Within limits, the resonant vibrations of the tube may be adjusted, or fine tuned, by varying this inside tube length slightly.
A panpipe, or pan flute, is made up of many separate resonant tubes, of different lengths to generate different tones, secured together side-by-side. The top ends of the tubes are open and generally aligned, and the bottom ends of the tubes are closed. The person playing the instrument holds it with the tubes generally aligned upright, and blows the activating air streams somewhat horizontally cross-wise to the open tube ends.
By selecting and/or adjusting the lengths and/or diameters of the tubes, the panpipe may be set up to play notes of a musical scales. A simple panpipe may have tubes of given fixed inside lengths, to produce only the tone preset for each tube; and such a panpipe provides for no adjusting or tuning of these tones.
For more expensive quality panpipes, some tuning may be provided. One basic means of tuning is to fill part of each individual tube interior, above the closed end, with a solid core of wax or like material; and to shave off the upper face portion of the material to the interior column height desired for producing the desired tone. This is done with a boring tool inserted into the tube from the open top end. As variations may exist in the inside tube diameter, merely boring to a specific column height may not produce the correct tone. Consequently, when the actual column height approaches that expected, the tube will be fine tuned by ear by alternately sounding it in resonance, and subsequently by minutely removing material, until the tone produced is true.
This tuning sequence may be quite perplexing since, one cannot simultaneously activate the tube and remove excess material, but these steps must be alternated; and should one remove too much material, additional material must be added to the tube interior and the tuning process repeated again.
This type of tuning also does not readily allow for individual or after market tuning of the tube, by anyone not having the skills and/or equipment needed for such a task.
When considering that a panpipe may have twenty four or more separate tubes, with each expected to produce a different properly tuned tone, this tuning sequence proves to be very time consuming and expensive.
Another means for varying the tone of an individual panpipe tube is with a closure plug inserted into an otherwise open bottom end of the tube. In one form, the plug may be sized to be inserted to some particular debth; while in another form, the tube may have some built-in stop to position the plug at one specific location. However, fine tuning to precise and/or different tones with such means is difficult, as controlled minute shifting of the plug is difficult.
A means for fine tuning an individual panpipe tube includes inserting a closure plug into the otherwise open bottom end of the tube, and adjusting the axial position of the plug minutely with a threaded screw connected to the plug. Several drawbacks exist within known versions of this, including: (1) when the plug can be axially adjusted within the tube, it may not be sufficiently tight to seal the tube; while (2) it may not be possible to tighten the adjusted plug for effectively sealing and locking it in the adjusted position, without at least partically disassemblying the overall panpipe structure.